powerpc: kernel/kgdb.c: Fix memory leakage
powerpc: kernel/kgdb.c: Fix memory leakage

the variable backup_current_thread_info isn't freed before existing the
function.

Signed-off-by: Cong Ding <8001b54ad539330acc19ca3e17ac1f04f07b36a6@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas